Oxidative dehydrogenation of n-butene, which is used to produce 1,3-butadiene that is gradually increasing in demand in petrochemical markets, produces 1,3-butadiene and water after reacting n-butene with oxygen, and is thermodynamically favorable because water, which is stable, is produced, and also the reaction temperature may be reduced. If a C4 mixture or C4 raffinate-3 containing impurities such as n-butane is utilized as the supply source of n-butene, the value of surplus C4 fractions may be advantageously increased.
As mentioned above, the oxidative dehydrogenation of n-butene (1-butene, trans-2-butene, cis-2-butene) is a reaction in which 1,3-butadiene and water are produced after a reaction between n-butene and oxygen. Oxidative dehydrogenation, however, is accompanied by many side-reactions, such as complete oxidations, which are expected to occur because oxygen is used as the reactant, and thus the development of catalysts which maximally suppress such side-reactions and increase the selectivity for 1,3-butadiene is regarded as of the utmost importance. The catalysts known to date used in the oxidative dehydrogenation of n-butene include ferrite based catalysts, tin based catalysts, bismuth molybdate based catalysts, etc.
Among these, the ferrite based catalysts have different catalytic activities depending on the kind of metal which occupies divalent cation sites of a spinel structure, and furthermore, zinc ferrite, magnesium ferrite, and manganese ferrite are known to be effective in the oxidative dehydrogenation of n-butene, and zinc ferrite is particularly reported as enabling there to be increased selectivity for 1,3-butadiene compared to when using ferrite catalysts of other metals [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., vol. 51, pp. 235 (1989)].
Reported in some patents and pieces of literature is the use of zinc ferrite based catalyst in the oxidative dehydrogenation of n-butene, in which in order to increase the reaction activity and lifetime of the zinc ferrite catalyst used in the oxidative dehydrogenation, pretreatment and post-treatment, including adding an additive to the catalyst, are carried out, so that 1,3-butadiene can be obtained in higher yield over a long period of time [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., vol. 51, pp. 235 (1989)/L. J. Crose, L. Bajars, M. Gabliks, U.S. Pat. No. 3,743,683 (1973)/E. J. Miklas, U.S. Pat. No. 3,849,545 (1974)/J. R. Baker, U.S. Pat. No. 3,951,869 (1976)]. In addition to the above zinc ferrite catalyst, the use of manganese ferrite catalyst for oxidative dehydrogenation of n-butene is reported in some patents.
In the oxidative dehydrogenation of n-butene, the zinc ferrite catalyst is problematic because reproducibility may be deteriorated by the addition of metal oxides used in order to prevent inactivation and by the acid treatment, and also complicated post-treatment procedures are required. Further, the manganese ferrite catalyst should be maintained at high temperature upon co-precipitation in order to exist in a pure spinel phase and decreases the yield of 1,3-butadiene compared to when using zinc ferrite.
In addition, the oxidative dehydrogenation of n-butene is problematic because the yield of 1,3-butadiene is lowered when the reactant contains a predetermined amount or more of n-butane [L. M. Welch, L. J. Croce, H. F. Christmann, Hydrocarbon Processing, pp. 131 (1978)]. Thus, in the above conventional techniques, such problems remain unsolved when oxidative dehydrogenation is carried out using only pure n-butene (1-butene or 2-butene) as the reactant. Hence, various pieces of literature or patents related to catalysts and processes for producing 1,3-butadiene from n-butene using oxidative dehydrogenation as above and processes based thereon, including using pure n-butene as the reactant, are disadvantageous because a separation process for extracting pure n-butene from a C4 mixture should be additionally performed, thereby drastically reducing economic efficiency.